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my chlorine level off the chart. please help!

I have a new SWG pool...about a month old. SWG only started up last week. But before it did, my FC level went down to 0. I put in some salt shock last weekend and turned off the SWG. Went on business trip. Came back today. Tested water and was suprised at my numbers. Can someone help? My numbers seem to be off the charts.

First, make sure the SWG is really off. It is fairly easy to have the percentage too high, particularly if your water is fairly cold (chlorine demand can be very low when the water is cold).

The FC level should drop measurably day by day if you are getting any sunlight. If the water is particularly cold it might take a while to get down to reasonable levels. Keep an eye on it so you can turn the SWG back on when the level gets more reasonable.

The PH test tends to read much higher than actual when the FC level is that high, so your PH might be alright. When the FC gets down to 15 or below start believing the PH test. If this is a plaster/pebble pool you have a problem because new plaster can raise the PH quite rapidly, but the PH test doesn't work at high FC so you can't tell how much acid to use.

You could think about getting some chlorine neutralizer. I wouldn't worry about it if you have vinyl or fiberglass, but with paster/pebble if the FC doesn't go down soon you could have PH problems and that might make it worth the expense.

Also, your TA is a little high. That is also going to push your PH up over time. With a SWG I suggest TA around 70-90. This isn't normally a big deal, since managing the PH with acid will bring the TA down over time. However it increases the worry about checking the PH fairly soon.

some additional information: i actually had the swg off after i shocked the pool, but had my wife turned it on last night at 50%. but why does it take so long for the chlorine level to go down? I would expect it to be down to normal level a couple of days after shock. And my I have a plaster pool.

Questions:
- should i add acid now or should i wait for the chlorine level to go down (either by itself or adding neutralizer)?
- how much neutralizer should i add to bring chlorine level down to a normal range?

With the SWG off and a CYA level around 50 you should lose somewhere around half of your FC each sunny day. The exact amount could be very different and will depend first on how much direct sunlight the pool gets and secondly on what the water temperature is. If the SWG is on then it might well replace any FC that was lost and the level could continue to go up. The other possibility is that you might have shocked the pool to far too high a level and it has taken this long to get down to a reasonable level.

If you have a sense of how frequently you have been adding acid then you could continue adding acid at about that rate. With the SWG off the FC level should fall below 15 in a day or two, in which case you should be able to wait for it to fall. If the FC hasn't fallen significantly by late afternoon then I would try the chlorine neutralizer. There should be directions with the neutralizer that tell you how much to use. I would aim for a FC level of around 10-15 and then let it fall naturally from there.

I know this topic has been idle for a few weeks, but I think it may be realted to an issue I've been having with testing my spa.

newb said he used "salt shock." I've not seen this term used before. Is this a chlorine based shock or a non-chlorine shock based on Potassium Monopersulfate (MPS) ?

The reason I ask is that I have been using MPS in my spa, and even after a week with no MPS (chlorine only) and daily spa use, my FAS-DPD is still really off! OTO and test strips all agree that I have 2-3 ppm TC, but FAS-DPD says I have 11ppm FC and 3ppm CC even when using the Taylor Deox reagent (R-0867) to remove the MPS interference per Taylors instructions.

I'm beginnig to believe that non-chlorine shock (MPS) has a significant FAS-DPD interference for a much longer period of time than is implied in the usage instructions and the Taylor interference remover is only able to deal with a small trace of residual MPS.

PS I have the PS-234 test kit, but my FAS-DPD reagents are from TFkits and Taylor and are only about a month old. I'm going to order up some additional reagents (I've been going through a lot testing the new spa ) just to be eliminate the reagents as a possible explaination for my results.